Abstract:
An accurate time scale derived from benthic Foraminifera delta (super 18) O is crucial to paleo-oceanographic studies. In global oceans, there are few continuous delta (super 18) O records for benthic Foraminifera that span the past 5 Ma and have a time resolution better than 5 ka. Such representative profiles have been established for ODP Site 659 in the Atlantic and ODP Site 846 in the East Pacific, but are still absent in the "Western Pacific Warm Pool", an area that plays an important role in global climate change. Based on benthic Foraminifera delta (super 18) O from ODP Site 1143 in the southern South China Sea, we establish a 5 Ma astronomical time scale for the Plio-Pleistocene in the West Pacific with a time resolution of -2,000-3,000 years. The phases are fixed at 8 ka and 5 ka for the obliquity and precession bands, respectively, and have been applied throughout the whole record. Obliquity and precession are calculated and treated as tuning targets. An automatic orbital tuning method was used in this study, which is more efficient than what was used at ODP Sites 659 and 846. Results show that the 190.77 m long deep-sea sediments in the South China Sea have recorded a paleo-oceanographic history of -5.02 Ma, corresponding to 191 glacial-interglacial cycles. The tuned Brunhes/Matuyama paleomagnetic polarity reversal agrees well with the age of 0.78 Ma previously obtained. The tuned ages for several planktonic foraminiferal Mo-events also agree well with published dates, and new ages for some other events in the South China Sea are also estimated. The sedimentation rates calculated with this new time scale indicate that 2.9 Ma is a threshold for the sedimentation rate in the location of Site 1143. Before this time, the average sedimentation rate was -39.5m Ma, with a small amplitude of -50 m Ma. After this time, the average sedimentation rate jumped to -65.4 m Ma, with an amplitude as large as 200 m/Ma. In addition, sedimentation rates in the southern South China Sea were higher during glacial periods or stadials, but lower during interglacial periods or interstadials, especially in the late Pleistocene period. This feature might be related to global ice volume changes, which caused differing erosion, denudation and transportation during glacial and interglacial periods.